There has been known an antenna core formed by shaping a soft magnetic metal powder with the use of a resin as a binder in view of easy shape machining.
In Patent Document 1, there has been disclosed an antenna core excellent in magnetic characteristics employing a nanocrystal magnetic powder or the like with the use of a thermoplastic resin as a binder. However, since an antenna core is produced by a hot press method with the use of a thermoplastic resin as a binder, an antenna core is not taken out from a mold if it is not fully cooled. Accordingly, when an antenna core is continuously produced, there is a problem such that it takes time for cooling, resulting in a poor productivity.
In Patent Document 1, a resin used as a binder is limited to a thermoplastic resin, while the Tg range of a thermoplastic resin, the range of mixing ratio of a magnetic powder and a thermoplastic resin, and the press pressure at a hot press procedure are further limited. All of these limitations are to improve soft magnetic characteristics of a magnetic powder or to prevent soft magnetic characteristics from being deteriorated by applying the unnecessarily higher pressure to the magnetic powder. That is, in the conventional technical knowledge, when a thermosetting resin is used as a binder, soft magnetic characteristics of the magnetic powder are considered to be deteriorated due to shrinkage stress of a resin during a curing process. Accordingly, in order to avoid such deterioration, a thermoplastic resin is used, while the Tg range of a thermoplastic resin, the range of mixing ratio of a magnetic powder and a thermoplastic resin, and the range of press pressure at a hot press procedure are further limited.
In Patent Document 2, there has been disclosed an antenna core excellent in impact resistance composed of an insulating soft magnetic material having various soft magnetic metal powders and various organic binders. However, in Patent Document 2, there has been described only the use of “a Fe—Al—Si alloy powder” and “a polyurethane resin as an organic binder”, and “such a core is produced by laminating a sheet-like core material having a thickness of 1 mm, that is, a sheet,” but details of the soft magnetic metal powder and the organic binder are not disclosed. Accordingly, respective details of the soft magnetic metal powder and the organic binder used for the antenna core are not clear.
Patent Document 1: Japanese Patent Laid-open No. 2004-179270
Patent Document 2: Japanese Patent Laid-open No. 2005-317674